The sudden loud noise of steps gave me a start. It was a group of young children who were running in my direction, and then they passed by me with such energy that I had to step off the pavement to avoid being knocked over. They were shouting and laughing, as if that day just happened to be the happiest of their whole lives. A boy who was a little behind the rest reached out his hand and, without slowing down, tugged at a piece of an advertising poster which had started to come away from the wall in a failed attempt to rip the whole thing off. When I looked at it afterwards I saw the face of panic that remained, the perfect illustration of how awful it feels to be well and truly ripped off. Some walls really can talk…